An avalanche photodiode (APD) is a type of photosensitive semiconductor device in which light is converted to electricity due to the photoelectric effect coupled with electric current multiplication as a result of avalanche breakdown. APDs differ from conventional photodiodes in that incoming photons internally trigger a charge avalanche in APDs. Avalanche photodiodes are typically employed in laser rangefinder applications and long-range fiber optic telecommunication applications.
One of the parameters that impact the applicability and usefulness of APDs is dark current, which is a type of relatively small electric current that flows through a photosensitive device, such as a photodiode, even when no photons are entering the photosensitive device. Dark current is one of the main sources of noise in photosensitive devices. Consequently, dark current is a limiting factor for Ge/Si APDs in high-speed optical communication applications.
There is, therefore, a need for a novel and non-obvious design of APDs that reduces the effect of dark current to achieve high performance.